Pocket-type synthetic resin-made separators are known for use in lead-acid storage batteries. Conventional pocket-type separators are used to contain either a positive electrode plate or a negative electrode plate so that the counter-electrode plate not contained in the pocket-type separator can be stacked upon and aligned with the outer surface of the separator to provide a plate assembly which makes up at least one cell element.
However, whether a positive electrode plate is contained in the conventionally known pocket-type separator or stacked on the outer surface thereof, it has been common practice to interpose a glass mat between the synthetic resin-made separator and the positive electrode plate in order to prevent active material from flaking off the positive electrode and deterioration of the separator from oxidation by contact with oxygen generated from the positive electrode plate. Moreover, in manufacture it is difficult to insert and position the glass mat so as to properly interpose the glass mat coordinately between the positive electrode plate and the surface of the pocket-type separator. A further problem results from the fact that both side edges of the positive electrode plate are likely to contact both side edges of the synthetic resin-made separator or the immediate adjacent area thereof. As a result, the separator can have physical damage or material deterioration from oxidation which results in separator failure and shorting out of the cell.
When a negative electrode plate is placed in the pocket-type separator, it is not necessary to interpose a glass mat between the negative electrode plate and the inner surface of the separator. However, before a positive electrode plate is stacked on an outside surface of the separator, a glass mat is conventionally stacked on the outer surface of the separator and then the positive electrode plate stacked on the glass mat to provide a plate assembly. The use of the glass mat is to decrease flaking off of active material from the positive electrode and deterioration due to oxidation. It is extremely time-consuming, however, to stack these three different components, i.e., a pocket-type separator, a glass mat and a positive electrode plate, one after another in proper alignment with each other. Furthermore, it has been determined that during the stacking operation and subsequent handling operations involving the stacked plate assemblies and placement in a battery container or the like, the glass mat tends to at least partially move out of position or slip off completely making it difficult to achieve high productivity in the production of aligned stacked plate assemblies.
Japanese Kokai Utility Model Publication No. 57-23868 discloses a pocket-type synthetic resin-made separator for containing a negative electrode plate having a leaf-like glass mat bonded to the central region of an outer side of the separator. The glass mat bonded to the separator is narrower in width than the separator. This pocket-type separator can be prepared prior to alignment of an electrode to an outer surface of the separator thereby avoiding the need to stack on the outer surface of the separator a separately prepared glass mat at the time of stacking an electrode. However, disadvantages are still present with this structure. For example, both seal-bonded side edge portions of the pocket-type separator extend outward beyond both the side edges of the glass mat and, therefore, are exposed to external surroundings. These exposed or uncovered portions are likely to be damaged when hit by a stacking or other battery assembling apparatus in the course of a battery manufacturing process involving the stacking of a positive electrode plate on the pocket-type separator and placement of the formed plate assembly into a battery container to provide a storage battery. Further, as the finished battery product is relocated for use and in the course of use of the battery, the exposed side edge portions of the separator become oxidized, and thus deteriorate, resulting in the breakage and flaking off of active material from the electrode plate and the shortening of the battery's life or premature failure of the battery. Additionally, when a continuous manufacturing process is used in which a pocket-type separator and a positive electrode plate are stacked one upon another by means of a stacker to continuously produce plate assemblies, the process is often hampered due to the difference in height existing between the side edges of the pocket-type synthetic resin-made separator and the side edges of the glass mat stacked on or bonded to the outer side surface of the separator.